The proposed study will define the role of basal lamina, its constituent glycosaminoglycan (CAG, acid Mucopolysaccharide), and specific stromal tissue in mammary morphogenesis occurring post-natally and during pregnancy. The overall rationale for this research is that such a characterization will provide the basis for future studies examining whether the growth or invasiveness of mammary cancer involves abnormalities in the stromal requirement, or in the synthesis, degradation, or distribution of basal lamina GAG. This proposition is strengthened by the finding that mammary carcinoma can be induced by mammary mesenchyme to acquire differentiated elements and to organize materials tentatively identified as GAG (4), and that in human specimens basement membrane material thought to be GAG is altered in mammary carcinoma.